51. Wastewater Decimates Minnows

Birth control pills work wonders in preventing human reproduction. Unfortunately, they’re also effective on an unintended target—fish. In fact, the synthetic estrogen in contraceptives can wipe out entire fish populations, according to Karen Kidd of the Canadian Rivers Institute at the University of New Brunswick. Her findings, reported in the Proceedings of the National Academy of Sciences in May, suggest that tougher sewage treatment could safeguard the little swimmers.

Previous studies linked wild male fish possessing uniquely female characteristics—production of eggs and the egg protein vitellogenin (VTG)—to the presence of natural and synthetic estrogens in waterways downstream of sewage outfalls; one estrogen source is the hormone that women excrete in their urine.

For three years, Kidd and company added the same synthetic estrogen as in the pill to a research lake operated by Fisheries and Oceans Canada to mimic the chronic low levels released by treatment facilities. During the study, all the lake’s male fathead minnows began producing eggs and VTG, the female fish’s egg development became delayed, newly hatched fish disappeared, and by the end, minnows were all but locally extinct. Kidd says the short-lived minnows were the first to go, but larger fish, many of which feed on minnows, would most likely have been affected over time.

While more advanced secondary and tertiary sewage treatments, including measures like activated charcoal filtration, can remove 90 to 100 percent of the estrogen in wastewater, some North American cities employ only primary treatment. “A lot of our regulations focus on persistent chemicals like DDT,” Kidd says. “We need to pay more attention to nonpersistent ones in wastewater because fish are being continuously exposed, and even at low levels, that can have serious consequences.”